06 Silverado with 6.0 Reduced Engine Power

We have an 06 with the dreaded reduced engine power. P1516. It has had the Throttle Body replaced last summer. Now it is acting up again and GM is not sure how to fix it. New Throttle Body connector was recomended. Connector is on, as well as a new Throttle Actuator Control Module to no avail. All grounds have been cleaned and reconnected. GM is stumped on this as they have 3 others doing this same thing here locally.